Physical Appearance

All these years since the ROC stand down makes it difficult to find photographs of the surface features of a post ready for action. These two stills from the film 'Sound an Alarm' show all the salient features.

This is a typical view of the exterior of a ROC monitoring post. A 20 ft vertical ladder leads to an underground chamber 7ft x 16ft x 7ft high. This houses the observers and their instruments and welfare facilities. Conditions were very primitive, there was no running water, gas or mains electric. The only communication with the outside world was the Tele-Talk device, connected to ROC Group HQ and the Carrier Warning Receiver. No telephone was provided.

When not in a state of readiness the Radiac Tube and Bomb Power Indicator (BPI) baffle would be removed and replaced by blanking plates. The Ground Zero Camera would be removed and taken inside.

Originally the only air supply was via two louvered vents, one on each end of the chamber, which meant it could be quite damp. Latterly some posts were fitted with power operated fans. Despite posts being located on high ground they were often below the water table and collected water that had to be pumped out before it could be manned. One has to admire the dedication of people prepared to lock themselves away in these conditions.

This picture was taken from the step looking down into the post. The grating at the bottom covers the water sump. Next to this is a hand operated pump and a vertical pipe to expel the water. The toilet door is on the right and the observation room door at the bottom of the photograph. The hatch counterbalance can be seen at the top.

 

Instrumentation

A Ground Zero Indicator (GZI) shown above was employed to record the position of a nuclear detonation. This consisted of 4 pinhole cameras in one enclosure. One of the pinholes can be seen in this photograph. The camera is bolted onto a bracket on the outside of the post on the entrance hatch. Special light sensitive paper recorded the position and size of the fireball. This gives the direction bearing from North to the fireball and an elevation reading.

Within the post, a Bomb Power Indicator (BPI), a pressure detector displays the peak pressure of the blast wave. It's needle stays at the highest pressure recorded until reset by hand.

Above ground there is a baffle plate to collect the pressure wave mounted on top of the pipe down into the post. When the post was not manned the baffle was replaced by a seal.

After bomb a detonation, the direction, elevation and spot size of the fireball and reading of the pressure wave on the BPI would be passed to ROC Group HQ using the Tele-Talk unit or Radio.

Group HQ would use the direction information from two or more posts to determine the exact point of detonation by using triangulation. Once the position of the detonation had been calculated, Group HQ would estimate the yield (size) of bomb from the pressure wave reading. The height of the centre of the fireball could be determined from the elevation readings. A detonation at ground level (ground burst) would create fallout. Whereas a similar bomb exploding so its fireball did not touch the ground (air burst) would create little fallout. It was assumed the enemy would use a combination of air and ground burst weapons.

 

From the safety of the underground room the observer would monitor radiation levels using a Radiac Survey Meter (Geiger counter) head pushed up a tube extending from a flange in the ceiling up to the surface and into the protective grey tube. Regular readings of the radiation from any subsequent fallout from a bomb would be relayed to Group HQ enabling them to plot the progress and path of the fallout plume.

Selected posts had equipment to allow them to make meteorological reports for ROC Group HQ. These could supplement or replace meteorological office weather forecasts used to determine the likely path of fallout.

 

Warning Function

ROC Posts had both a warning and monitoring role. The post’s carrier receiver would alert them of the Attack Warning then using the hand powered siren the post personnel would sound the public Attack Warning.

If a Fallout Warning was issued from Group HQ either directly via the TeleTalk or relayed via the Carrier Control Point and Carrier Receiver, the post would sound a pyrotechnic maroon. Should the local external radiation reach a predetermined level the Post would sound the Fallout Warning irrespective of any received messages.

Due to the danger of using live maroons containing explosives during exercises a training kit was provided. Live maroons would be only issued in a War situation. The kit consisted of a dummy maroon containing bulbs to indicate the firing of each tube. The trainer was compatible with the normal controller and connected via six-way plug and long black wire, so the user would be at a safe distance from this powerful firework. The controller contain a dry battery, but an adapter (with the red wiring) allowed it to be operated from a car battery or post lighting / radio battery.

 

Post Clusters

Posts were typically grouped together in threes or sometimes four, to form a cluster. Each post was uniquely numbered within the Group area. The first post in each Group area would be designated 10. One post in the cluster was designated as the master post its number would end with a 0 or 5 and marked ‘M’ below and the remaining posts within the cluster numbered sequentially. This results in a numbering scheme like this in the York Group.

 

ROC Post Communications Overview

The primary means of communications was the TeleTalk device connected to a landline private circuit. The same private circuit delivered the carrier to the Warning Receiver in the post. Contrary to some belief there wasn’t a telephone in the post. Neither did it have any contact with the local police station via landline or radio.

When switched on the TeleTalk would be in listen mode on the private circuit. If the Group HQ operator spoke this would be heard at all the posts in the cluster. To speak back, a switch was depressed, and the observer spoke towards the loud speaker grill, the other posts in the cluster would hear the reply to Group. To initiate a message to Group the observer would press a call button to attract the operator’s attention. The posts in the cluster could talk amongst themselves without involving Group as the arrangement is very similar to an Intercom.

The master post in the cluster was equipped with a radio as a backup to the failure of part or all of the private circuit linking the cluster to Group HQ. If the link back to Group was severed but the links to the other post were working, the master post would gather the readings from the other posts and radio them onto group.

In 1981 a Home Defence Review had recognised the need to improve and update the communications and equipment in use in the ROC. During the life of the posts there were two distinct equipment eras, these are discussed in separate topics.